GB1070947A - Improvements in or relating to laser systems - Google Patents

Abstract

1,070,947. Lasers. AMERICAN OPTICAL CO. Aug. 4, 1964 [Aug. 5, 1963], No. 30426/64. Heading H1C. In an optically pumped laser the elongated solid active medium is surrounded by a cladding having a refractive index equal to or lower than that of the active medium and being such as to transmit energy at the optical pumping frequency and absorb optical energy at the laser emission frequency. A laser (10), Fig. 1 (not shown), comprises an elongated straight-sided cylindrical-shaped solid active medium (12) of neodymium-doped barium crown glass having flat end faces (16), (18) coated with reflective coatings (22). Surrounding the member (12) is a selectively absorbing cladding (20) of ferrous iron containing alumina-phosphate glass having a refractive index substantially the same as the active medium and containing an absorptive material to provide high transmission of optical energy at pumping wavelengths and at the same time high absorption at the 1.06 micron emission wavelengths of the laser. Thus, pumping optical energy at this wavelength and spontaneous emission which strikes the interface (26) will be absorbed and secondary emission will be avoided, photons travelling in the longitudinal direction being the only ones allowed. The cladding (20) also serves the purpose of optically immersing the laser and providing a gain in the pumping light density. The glass cladding may be soda-lime crown glass containing samarium trioxide or barium crown glass containing dysprosium. Other glasses which may be used as the laser active material are tri-valent ytterbium-doped glass and tri-valent hobnium-doped glass. Ruby may be clad with blue sapphire. The laser active material may be clad with a double layer, Fig. 3 (not shown), and Fig. 7 in which arrangement the active medium 62 is curved longitudinally and is provided with first and second cladding layers 64, 66 having equal refractive indices n 2 , n 3 which are slightly less than that of core 62, n 1 . The ray 67 will thus travel down the core 62 by internal reflection whereas rays 68 pass through layer 64 into layer 66 where they are absorbed. This arrangement may be used in a helically coiled travelling-wave type of amplifier (63), Fig. 6 (not shown), in which a double clad fibre component (60) is wound in helical form around drum (74) in the centre of which are positioned one or a plurality of pumping light sources (78). A reflective housing may encircle the drum. In Fig. 4 (not shown), a hollow cylindrically shaped laser member (84) is provided with absorbing layers (86), (88) on its inside and outside surfaces and within and around the laser member are disposed a plurality of light pumping sources (85), (87) and a cylindrical member (94) provided with reflecting layer (96). In Fig. 2 (not shown) the ends of the laser body are arranged at an angle # to the longitudinal axis of the body so that no light within the member (50), (51) will be internally reflected back along the length of the laser member but will be absorbed by cladding (52).